Re: [RFC PATCH 1/2] drm/hyperv: Add DRM driver for hyperv synthetic video device

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> +/* Should be done only once during init and resume */
> +static int synthvid_update_vram_location(struct hv_device *hdev,
> +					  phys_addr_t vram_pp)
> +{
> +	struct hyperv_device *hv = hv_get_drvdata(hdev);
> +	struct synthvid_msg *msg = (struct synthvid_msg *)hv->init_buf;
> +	unsigned long t;
> +	int ret = 0;
> +
> +	memset(msg, 0, sizeof(struct synthvid_msg));
> +	msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
> +	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
> +		sizeof(struct synthvid_vram_location);
> +	msg->vram.user_ctx = msg->vram.vram_gpa = vram_pp;
> +	msg->vram.is_vram_gpa_specified = 1;
> +	synthvid_send(hdev, msg);

That suggests it is possible to define multiple framebuffers in vram,
then pageflip by setting vram.vram_gpa.  If that is the case I'm
wondering whenever vram helpers are a better fit maybe?  You don't have
to blit each and every display update then.

FYI: cirrus goes the blit route because (a) the amount of vram is very
small so trying to store multiple framebuffers there is out of question,
and (b) cirrus converts formats on the fly to hide some hardware
oddities.

take care,
  Gerd